1. Field of the Invention
The present disclosure relates to a liquid treatment apparatus and method that perform a liquid treatment such as cleaning and etching to a substrate by supplying a treatment liquid to a lower surface of the substrate.
2. Description of Related Art
In a semiconductor manufacturing process, substrates such as semiconductor wafers are subjected to cleaning or etching with use of a chemical liquid in order to remove unnecessary films adhering to the front or back surface of the wafer (e.g., oxide films, nitride films, or resist films having been used as a mask). In general, a rinsing step and a drying step are subsequently performed after a chemical liquid treatment step using the same apparatus for performing the chemical liquid treatment step.
JP2007-287999A discloses a liquid treatment apparatus capable of executing the aforementioned process steps. The liquid treatment apparatus includes a spin chuck that holds the peripheral portion of a wafer and rotate it, and a front surface nozzle that supplies a treatment liquid to the central portion of the wafer upper surface, a back surface nozzle that supplies a treatment liquid to the central portion of the wafer lower surface. The front and back surface nozzles can supply a chemical cleaning liquid, a rinsing liquid such as deionized water, and a drying solvent such as IPA.
One of the foregoing unnecessary films is a natural oxide film (SiO2 film). When a wafer is cleaned with DHF (diluted hydrofluoric acid), a natural oxide film is removed so that bare Si is exposed. That is, a hydrophilic SiO2 surface is altered to a hydrophobic Si surface. After the DHF cleaning step, a DIW (deionized water) rinsing step and a spin-drying step are performed. When a hydrophobic surface having DIW thereon is dried, uneven drying is likely to occur, in other words, water marks are likely to occur. In order to avoid generation of water marks, an WA substituting step that substitutes IPA (isopropyl alcohol) for DIW is performed between the DIW rinsing step and the spin-drying step. If such an IPA substituting step is performed to the wafer lower surface by a method taught in JP2007-287999A, the IPA can hardly be spread over the wafer lower surface uniformly. This is because IPA has a low surface tension and is thus likely to drop by gravity. In addition, a large amount of IPA is required to cover the whole wafer lower surface.